Concrete Technology: Chemical and Mineral Admixtures Unit 2 Part 4

Que3.5. Write short note on quality control of concrete. 

Answer  1. The strength of concrete varies from batch to batch over a period of  time.  ue3.6. bandy the statistical quality control of concrete.  Explain common  language used in statistical quality control of  concrete.  Answer  Statistical Quality Control of Concrete  1. Statistical quality control  system provides a scientific approach to the  concrete  developer to understand the realistic variability of the accoutrements   so as to lay down design specifications with proper forbearance to  feed  for  necessary variations.  2. The acceptance criteria are grounded on statistical evaluation of the test  result of samples taken at  arbitrary during  prosecution. By  contriving a  proper  slice plan it’s possible to  insure a certain quality at a  specified rise.  3. therefore the  system provides a scientific base of acceptance when is not  only realistic but also restrictive as  needed by the design conditions  for the concrete construction.  Common language The common  languages that are used  in the statistical quality control of concrete.  1. Mean Strength This is the average strength  attained by dividing  the sum of strength of all the  cells by the number of  cells.  2. friction This is the measure of variability or difference between  any observed data from the mean strength.  3. Standard divagation  i. This is the root mean square  divagation of all the results, is denoted by  ii. Standard  divagation increases with  adding  variability.  iii. The characteristics of the normal distribution  wind are fixed by the  average value and the standard  divagation.  4. Measure of Variation  It’s an indispensable  system of expressing the variation of result.  ii. It’s anon-dimensional measure of variation  attained by dividing the  standard  divagation by the  computation mean and is expressed as 2. The sources of variability in the strength of concrete may be considered  due to variation in the quality of the  element accoutrements , variations  in  blend proportions due to batching process, variations in the quality of  batching and mixing  outfit available, the quality of supervision  and workmanship.  3. These variations are  ineluctable during  product to varying degrees.  4. Controlling these variations is important in lowering the difference  between the  minimal strength and characteristic mean strength of  the  blend and hence reducing the cement content.  5. The factor controlling this difference is quality control.  6. The degree of control is eventually  estimated by the variation in test  results  generally expressed in terms of the measure of variation.  

Que3.7. Step by step explain the American Concrete Institute   system of  blend design. 

Answer  Following are the  way in American Concrete Institute  system  1. Data to be Collected  Fineness modulus of  named fine  total.  ii. Unit weight of dry rodded coarse  total.  iii. Specific  graveness of coarse and fine  summations in SSD condition  iv. immersion characteristics of both coarse and fine  summations.  Specific  graveness of cement.  2. From the  minimal strength specified, estimate the average design  strength by using standard  divagation.  3. Find the water/ cement  rate from the strength and  continuity points of  view. Borrow the lower value.  4. Decide the maximum size of  total to be used. Generally for RCC  work 20 mm andpre-stressed concrete 10 mm size are used.  5. Decide plasticity in terms of depression for the given job.  6. The total water in kg/ m3 of concrete is determined, corresponding to  the  named depression and  named maximum size of  total.  7. Cement content is  reckoned by dividing the total water content by the  water/ cement  rate.  8. elect the bulk volume of dry rodded coarse  total per unit volume  of concrete, for the particular maximum size of coarse  total and  fineness modulus of fine  total.  9. The weight of CA per boxy  cadence of concrete is calculated by multiplying  the bulk volume with bulk  viscosity.  10. The solid volume of coarse  total in one boxy  cadence of concrete is  calculated by knowing the specific  graveness of CA.  11. also the solid volume of cement, water and volume of air is  calculated in one boxy  cadence of concrete.  12. The solid volume of FA is  reckoned by abating from the total  volume of concrete the solid volume of cement, CA, water and  entangled  air.  13. Weight of fine  total is calculated by multiplying the solid volume  of fine  total by specific  graveness of FA. 

 Que3.9. What do you mean by Rheology of fresh concrete?  Explain the parameters of Rheology. 

Answer  1. Rheology It may be defined as the  wisdom of the  distortion and  inflow of accoutrements , and concerned with  connections between stress,  strain, rate of strain, and time.  2. The term rheology deals with the accoutrements  whose inflow  parcels are  more complicated than of simple fluids( liquids or  feasts).  Parameters of Rheology Following are the parameter of rheology  1. Stability  It’s defined as a condition in which the aggregate  patches are held in  homogeneous  dissipation by matrix, and  arbitrary  slice shows the  same  flyspeck size distribution during transportation, placing and   contraction.  ii. The stability of concrete is measured by its  isolation and bleeding  characteristics.  2. Mobility  i. The mobility of fresh concrete is its capability to flow under  instigation  transfer, i.e., under mechanical stresses. The inflow is  confined by  cohesive,  thick and frictional forces.  ii. The cohesive force develops due to adhesion between the matrix and  aggregate  patches. It provides tensile strength of fresh concrete that  resists  isolation.  iii. The  density of the matrix contributes to the ease with which the  aggregate  patches can move and rearrange themselves within the  matrix.  iv. The internal  disunion occurs when a admixture is displaced and the  aggregate  patches  restate and rotate.  v. The resistance to  distortion depends on the shape and texture of the   total, the  uproariousness of the admixture, the water- cement  rate, and  the type of cement used.  3. Compactability  i. It measures the ease with which fresh concrete is compacted.  ii. Compacting  correspond of expelling  entangled air and  displacing the  aggregate  patches in a  thick mass without causing  isolation.  iii. Compactability is measured by the compacting factor test.  

Que3.10. Describe the Bingham model of Rheology of fresh  concrete. 

Answer  1. The inflow  geste of fresh concrete doesn’t conform to Newtonian  liquid.  2. The  rate of shear stress to shear rate isn’t constant but depends upon  the shear rate at which it’s measured, and may also depend on the  shear history of the concrete sample being delved .  3. still, at low shear rates that are important in practice, the   geste can be represented by a straight line which doesn’t pass  through- the origin, i.e., which has an intercept on the stress axis.  4. The intercept indicates the minimum stress below which no inflow occurs.  5. The fact that concrete can stand in a pile( as in the case of the depression  test) suggests that there’s some minimum stress necessary for inflow to   do at all.  6. The minimum stress is called yield stress and designated by the symbol  therefore the simplest inflow equation of concrete illustrated in 3.10.1 can be written as  7. This  fine relationship is called the Bingham model.  8. Bingham model relates the shear stress of the material expressed in  terms of its cohesion to plastic  density, and the rate at which the  shear  cargo is applied.  9. To establish a straight line, at least two points are  needed. Consequently,  the plasticity of concrete can not be defined by the single- point tests  that determine only one parameter, i.e., produce only single point, and   thus have to be used in combination with other tests to achieve a  better understanding of concrete rheology.  10. For  illustration, the Vee- Bee test can be used with compacting factor test  to measure mobility and compactability.  

Que3.11. Explain the affective factors of rheological  parcels  of concrete. 

Answer  Following are the affecting factors of rheological  parcels of concrete  1. Mix Proportion A concrete  blend having an  redundant  quantum of coarse   total will warrant sufficient mortar to fill the void system, performing in  a loss of cohesion and mobility.  2. thickness The  thickness of concrete, as measured by the depression  test, is an  index of the relative water content in the concrete  blend.  3. Hardening and harshening  Elevated temperature, use of  rapid-fire- hardening cement, cement deficient  in gypsum, and use of accelerating  cocktails, increase the rate of  hardening which reduces the mobility of concrete.  ii. The dry and  pervious  total will  fleetly reduce plasticity by   gripping water from the admixture or  adding  the  face area to be  bathe.  4. Aggregate Shape and Texture  i. The rough and  largely angular  total  patches will affect in advanced  chance of voids being filled by mortar,  taking advanced fine  aggregate contents and  similarly advanced water content.  ii. also, an angular fine  total will increase internal  disunion in  the concrete admixture and bear advanced water content than  well- rounded natural beach.  5. Aggregate Grading A well- graded  total gives good plasticity.  These  goods are lesser in the fine  total than in coarse  total.  6. Maximum Aggregate Size An increase in the maximum size of   total will reduce the fine  total content  needed to maintain a  given plasticity, and will thereby reduce the  face area to be bathe.  7. cocktails The  cocktails which have significant effect on the  rheology of concrete are plasticizers andsuper-plasticizers, airentraining  agents, accelerators and retarders.

Leave a Comment